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cos⁡[tan⁡−1{sin⁡(cot⁡−1x)}]\cos[\tan^{-1}\{\sin(\cot^{-1}x)\}] is equal to

Solution

✅ Correct Option: 1

Let θ=cot⁡−1x\theta=\cot^{-1}x, so cot⁡θ=x\cot\theta=x and sin⁡θ=11+x2\sin\theta=\frac{1}{\sqrt{1+x^2}}.

Now let ϕ=tan⁡−111+x2\phi=\tan^{-1}\frac{1}{\sqrt{1+x^2}}. Then the hypotenuse is 1+(1+x2)=x2+2\sqrt{1+(1+x^2)}=\sqrt{x^2+2}.

Hence cos⁡ϕ=x2+1x2+2=x2+1x2+2\cos\phi=\frac{\sqrt{x^2+1}}{\sqrt{x^2+2}}=\sqrt{\frac{x^2+1}{x^2+2}}.

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